1. Field of the Invention
Such adapters have been known for a long time. They are usually made for a bullet cartridge designated 0.22 LR (5.6.times.15 mm) with rim fire, the bullet barrel being excentrically disposed in the plug, parallel to the axis of the plug.
The adapter and its comparatively underpowered bullet cartridge are usually used for killing at short range still living felled game, in certain cases instead of a special pistol when hunting fox and badger, as well as in hunting varmint (crows, gulls, mink, rats etc.).
A short firing range does not require particularly high precision or a close hit pattern. The adapter can be short and the play between the plug and the cartridge chamber may be comparatively large without spoiling the result. Simple adapters according to the introduction can be quite satisfactory. As only one round generally needs to be fired in one connection, a shell extractor for the fired cartridge is usually lacking. After firing, the marksman takes the adapter out and knocks out the shell with a rod of some kind.
A problem is that shots at a longer range e.g. at sitting birds, require higher precision. The hits must sit well collected, e.g. within a circle of 25 mm diameter at 50 meters. In addition, the hit center must as closely as possible correspond to the point aimed at by the normal sighting gear of the weapon. Only in exceptional cases does an adapter according to the introduction meet these demands. The play of the plug in the cartridge chamber gives a wide spread to the shots. The barrels in a double-barreled shotgun are usually directed convergingly (as with a double-barreled sporting gun), which results in that an adapter in a left bore throws to the right, in a right bore to the left, in an upper bore below and in a lower bore above the sighting point.
2. Description of Related Prior Art
Attempts have oeen to solve at least some of these problems. The U.S. Pat. No. 2,641,860 thus describes a long adapter with a parted plug, the forward part being glidable about the bullet barrel and provided with a forward conical portion for engagement against the wall in the transition cone between the shot bore and the cartridge chamber. The glidability allows adjustment of the plug for cartridge chambers of different lengths. After adjustment the conical portion may be locked against the bullet barrel. The bullet barrel is also guided in the shot bore with the aid of three spaced bushes and four leaf springs which are radially adjustable at the central bush with the aid of set screws for setting the bullet barrel in correct alignment in the shot bore.
The construction of the known adapter is thus very complex and expensive. The alignment is also difficult for the user, and probably causes wide hit spread, since the three bushes at the ends and at the middle of the barrel, as well as the leaf springs, disturb the oscillation pattern of the bullet barrel in shooting in a manner difficult to control. It has been known for a long time that a bullet barrel shall be rigidly clamped at the chamber and otherwise free so that the barrel oscillations will be reproduced alike from shot to shot.